1. Technical Field
The present invention relates to a voltage measuring apparatus which detects a voltage of an assembled battery including a plurality of unit cells connected in series in order to output a desired voltage.
2. Background Art
For example, an electric vehicle or a hybrid vehicle includes a high voltage battery as a motor driving power source. Such a high voltage battery obtains a high voltage by connecting, in series, a plurality of unit cells of a secondary battery (storage battery) such as, for example, a nickel-hydrogen battery, a lithium battery or the like.
In charging or discharging all secondary batteries with the same power, if these secondary batteries have different deterioration conditions, the secondary batteries are prone to an overcharging condition or an overdischarging condition. Therefore, there is a need to check a charging condition of each unit cell to prevent the secondary batteries from being in the overcharging condition or the overcharging condition. Accordingly, a plurality (for example, 55) of unit cells are divided into, for example, 5 blocks (i.e., one block is composed of 11 unit cells), and a voltage of each block is measured in real time by a voltage detection IC provided in each block.
In this case, the voltage detection IC measures a voltage of unit cells (for example, 11 unit cells) of one block, and a detected analog voltage signal is converted into a digital signal by means of an A/D converter included in the voltage detection IC, which is then transmitted to a main microcomputer.
Here, if an abnormality occurs in the A/D converter included in each voltage detection IC, the voltage detected for each unit cell may not be converted into a digital signal correctly. For this reason, the main microcomputer may not acquire correct voltage information, which may result in impossibility of detection of an overcharging condition or an overdischarging condition of a secondary battery.
Therefore, there has been proposed a technique disclosed in, for example, JP-A-2006-304365 which detects an abnormality of an A/D converter quickly. In the technique disclosed in JP-A-2006-304365, a power supply outputting a predetermined output voltage is connected to each voltage detection IC, the output voltage is converted into a digital voltage by means of the A/D converter, and it is determined whether or not the A/D converter works normally by checking a match of the digital voltage value with the predetermined output voltage.
However, in the above-mentioned voltage measuring apparatus, a power supply used to determine the abnormality of the A/D converter is required in addition to a reference power supply used for the A/D conversion, i.e., the reference voltage, which results in higher production costs.